Engine size recommendation
I would like to have a set-up closer to 15-17mpg, is this possible with a 360? Is it possible with the 318?
I get 16.5 to 18 mpg around town and 21-22mpg on the hiway with my 360. BUT, I also have an A833OD tranny, this combined with 3.55 gears and a 27" tall tire has it turning a tick over 2000 rpm at 65 mph and when I am crusing at anything over 40 mph its in OD.
This engine is far from stock and I have spent a fair amount of time getting the carb dialed in for great mileage. When I first dropped it in the car I was getting 12 mpg. Based on 102 mph trap speeds it is making approximately 370 HP.
Here is my build;
Bottom End: zero decked block with 30 over KB107 pistons.
Heads: Stock magnum heads with 64cc chambers and MP R/T valve springs. Combined with an 0.040 head gasket I have a static compression ratio of 10.6:1. The closed chamber magnum heads provide excellent quench allowing the engine to run on 89 octane and I have used 87 in a pinch but have to be careful getting on it at the lower rpms with 87.
Cam: Comp XE268H. 224/230 duration at 50 with .509/.512 lift (this is more than advertised because of the magnum 1.6:1 rocker ratio). Engine pulls strong from 1500 rpm to 6000+ rpm.
Intake, Exhaust and Carb : I have a Professional Products Crosswind high rise dual plane intake, 1 5/8 headers, 2.5" exhaust with turbo mufflers and an X-pipe. After trying a bunch of different carbs I have settled on a Holley 670 Street Avenger, this carb more than any thing else contributed the most to the decent mileage (it picked up 5 mpg with no tuning compared to a Road Demon 725 or a Holley 3310 750). Also, there is no loss of power as measured by the butt dyno compared to the bigger carbs I tried, the smaller carbs I tried did have a noticeable drop off in power on the top end. BTW, the 370 HP estimate was derived from 1/4 mile runs with a 600 CFM carb.
My Barracuda is a nice weather daily driver between April and the first time the roads are salted in the late fall. I typically put 7-8k miles per year on it. My other vehicle is a Dakota 4x4 which with a v6 gets about the same mileage.
